1. Field of the Invention
The present invention relates to a rolled threaded filter bowl for use with medium pressure filters.
2. Description of the Prior Art
Medium pressure filters such as those used in hydraulic oil systems for hydrostatic drives must withstand pressures greater than 400 PSI. Furthermore, they are subject to repeated or cyclic applications of pressure. Conventional medium pressure filters include a metal bowl or canister typically made from steel and a filter element contained within the bowl. The bowl is attached to a filter head which is in fluid communication with a conduit through which the hydraulic fluid passes. Such bowl and filter element arrangements are manufactured as a single unit. The open end of the canister is threaded to engage with the filter head. Such filter are known in the art as "spin-on" filters. The entire bowl with filter element thereon is spun onto the filter head and then is in fluid communication with the conduit.
When the filter element has become fouled from use and reaches its usable life, the entire filter including the filter element and bowl are removed from the filter head and is then disposed of. Because the filter element and bowl constitute a single unit, disposal of the filter element also dictates disposal of the filter bowl. Disposal of both portions of the conventional spin-on filter, namely the fouled filter element and the metal bowl, is wasteful in that the bowl is not fouled and is environmentally unsound.
One solution to this problem is to employ a reusable extruded metal (e.g., aluminum) bowl having threads for engagement with the filter head. Such threads are conventionally machined into the exterior surface of the metal. Because of the machining process, the wall of the bowl in the area of the machined thread must be relatively thick, for example, about 1/2 inch. Attempts to machine threads on thinner walled bowls typically fail because the machining process cuts completely through the thickness of the bowl wall rendering the bowl useless.
It is desirable to minimize the number of threads on the bowl. Fewer threads requires less threading and rotating of the bowl during installation and removal. However, when the thread number is low, the thread height (valley to peak) must be increased. Greater thread height requires that the walls of the bowl be relatively thick to allow sufficient material to be cut to create the threads. Medium pressure filters do not require such relatively thick-walled filter bowls to withstand the internal pressure of filtration. Thus, thick-walled filter bowls use an unnecessary amount of metal with respect to their pressure ratings only so that threads may be machined therein.
Furthermore, machined threads can detrimentally alter the metallurgical properties of the metal of the bowl. Such threads can also induce stress within the bowl. Threads produced by machining typically have rough surfaces and thus are easily filled by dirt, dust and the like.
Accordingly, a need remains for a thin walled threaded filter bowl which is reusable and easy to install yet can withstand medium pressures.